This invention relates to toaster oven appliances and, in particular, to an interactive user programmable control circuit for controlling and operating a toaster oven appliance and for providing improved accuracy and performance repeatability thereof.
Toaster oven appliances have by their nature been small appliances which have used simple electrical components to provide function and temperature control. Temperature sensing within the food chamber or compartment is typically by means of temperature varying resistance elements such as thermistors. Temperature selection is typically provided by means of a potentiometer which is adjustable by the user to a selected temperature by means of a calibrated scale. Function selection is normally provided by a multi-pole, multi-throw rotary switch which establishes a required electrical connection of discrete elements for each of the available modes of operation. The modes of operation commonly provided on contemporary toaster ovens include BAKE, BROIL and TOAST. Some of the more recent toaster-oven designs include a TIMER function which can be combined with the standard functions or modes to provide the functions of TIME BAKE and TIME BROIL. Adjustment of the timer function has also been by means of a calibrated potentiometer which can adjust a time constant in a relaxation or regenerative oscillator or set a mechanical timer.
The known toaster-oven appliances have, therefore, generally used analog control circuits. However, such circuits do not provide a great degree of accuracy or repeatability since they rely on user adjustments of continuously variable components such as potentiometers and, to some extent, on the regulation of the power supply and the voltage levels in the control circuit.
A toaster oven manufactured by the assignee of the present invention, and designated as Model No. 2000, features a source of stable reference voltages which are applied to the adjustable timer and temperature potentiometers. The use of accurate reference voltages eliminates one of the causes of inaccuracy and lack of repeatability.
The Model No. 2000 toaster oven appliance also includes circuitry for comparing a temperature sense voltage with voltage signals which are derived by the use of predetermined relationships which are a function of the selected mode of operation and the user selected temperature. While the Model No. 2000 represents an advance in toaster oven technology, it fails to provide the accuracy and repeatability and, therefore, the predictability in the use of toaster oven appliances. Additionally, the Model No. 2000, as the other known toaster oven appliances, fail to provide an interactive display which assists the user in making proper data entries, and which displays data such as the selected mode of operation, the selected temperature and the time remaining in a timed mode of operation.
In larger microwave ovens, microprocessor-based logic circuitry has in recent years been displacing electro-mechanical timers and other control elements. Microprocessor-based control circuits for microwave ovens are disclosed in U.S. Pat. No. 4,011,428; "Amana's Oven With a Brain", Appliance Manufacturer, Page 33, July 1975; "LSI Controls Gaining In Home Appliances", Electronics, page 91, Apr. 14, 1977; "Single-Chip Microprocessor Rules the Roast", Electronics, page 105, Dec. 9, 1976. A preprogrammed microwave oven controller is offered by Texas Instruments and designated by its product number TMS 1117, and described in "TMS 1000 Series One-Chip Microprocessors From Texas Instruments", Bulletin Cl-304, 1978.
The microwave oven control circuits offer programmable sequences of cooking cycles, temperature control cooking as well as cooking speeds. However, microwave ovens do not use the same heating and sensing elements found in toaster ovens. Additionally, the modes of operation are normally different in the two appliances although in some instances there is some overlap. Because of their greater size, microwave ovens have been used to prepare small as well as larger meals, while toaster ovens have traditionally been used to make toast, and bake, broil or cook small meals. Thus, while manufacturers have commenced to use microprocessor-based circuitry in the large and more expensive appliances, it is not until now that a microprocessor-based control circuit specifically adapted for toaster ovens has been developed.